Yes, Admissions in engineering colleges in ap done based on the rank of eamcet rank, so the better rank you get the better colleges you get. Yo should get a minimum of 40 marks to qualify in eamcet. Also remember all the colleges will not consider score of eamcet there are some private universities like klu,gitams which have their own entrance exams. Also note the eamcet score is not elgible in ouside states to get admission in engineering.